In many electronic applications; a reference voltage having a very low temperature coefficient is required. Band-gap voltage reference circuits have been developed to fulfill this need. The nominal temperature coefficient (TC) of a silicon diode is −2 mV/° C. However, TC is inversely proportional to the current density J in the diode. By manipulating the current densities through two diodes and taking the difference in forward bias voltages, one can create a circuit with a well-defined positive TC. This is then added to the forward bias voltage of a third diode. The positive TC of the diode pair cancels the negative TC of the third diode and one is left with a circuit with zero TC.
Referring to band-gap voltage reference circuits having bipolar transistors, FIG. 1 depicts a conventional bandgap circuit 100. The circuit 100 contains two bipolar transistors 102 and 104. The two bipolar transistors 102 and 104 have voltages VBE and ΔVBE in relation. VBE has a negative temperature coefficient, which is −2 mV/C. ΔVBE has a positive temperature coefficient, which depends on the current density of the two bipolar transistors 102 and 104. The relation is expressed by the following equation:ΔVBE=(KT/q)*ln(J2/J1)
The bandgap circuit 100 operates by using PTAT and CTAT currents from two branches to derive a constant current into the resistor, which generates a constant reference voltage. In circuit 100, three resistors 106, 108 and 110 must be matched. Thus, the conventional bandgap circuit 100 is a complex circuit.
Further, there are many PMOS and NMOS transistors that need to be matched to obtain a low temperature-dependent reference voltage. Accordingly, a need exists for a simplified temperature-independent reference voltage circuit.
In view of the foregoing, a need exists to overcome the problems with the prior art as discussed above.